1. Field of the Invention
The invention relates to a welding structure and a welding method. More particularly, the invention relates to technology that improves the positioning accuracy of sheet-shaped members when welding the members together.
2. Description of Related Art
Japanese Utility Model Application Publication No. 5-78376 (JP-U-5-78376) and Japanese Patent Application Publication No. 2003-103376 (JP-A-2003-103376), for example, describe technology in which, when welding sheet-shaped members together, a plurality of circular holes are provided in one part to be welded, and a plurality of round protruding portions are provided, in positions corresponding to the circular holes, on another part to be welded. The other part is positioned with respect to the one part with the protruding portions fitted into the circular holes, and the welding is then performed.
When positioning the sheet-shaped members by fitting the plurality of protruding portions into the plurality of circular holes, as in the technology described in JP-U-5-78376 and JP-A-2003-103376, it may be difficult to ensure the necessary accuracy of the circular holes and the protruding portions during the positioning of the sheet-shaped members.
One example of a case in which it is difficult to ensure the positioning accuracy of the sheet-shaped members will now be described with reference to FIGS. 10A to 10C. FIG. 10A is a view of a welding structure when a sheet-shaped member 1 is welded to a sheet-shaped member 2. When welding the sheet-shaped member 1 to the sheet-shaped member 2, circular holes 3a and 3b are opened in two locations in the sheet-shaped member 1, and round protruding portions 4a and 4b are provided in two locations, in positions corresponding to the circular holes 3a and 3b, on the sheet-shaped member 2. As shown in FIG. 10A, the sheet-shaped member 1 is positioned with respect to the sheet-shaped member 2 while the protruding portions 4a and 4b are fitted into the circular holes 3a and 3b, respectively, and welding is then performed.
In FIG. 10A, the sectional shape of the sheet-shaped member 1 is formed in two opposing crank shapes with a common side. Hereinafter, this sectional shape will be referred to as a “hat-shaped cross-section”, and a sheet-shaped member having such a sectional shape will be referred to as a “hat-shaped cross-section part.” In other words, a hat-shaped cross-section part is a sheet-shaped member having a groove formed in the length direction.
The sectional shape of the hat-shaped cross-section part (i.e., the sheet-shaped member) 1 may change in a direction perpendicular to the direction in which the groove is formed (i.e., perpendicular to the depth direction of the groove), as shown in FIGS. 10B and 10C, due to a change in which a bend in press-forming returns (so-called spring back) or the like. In this case, when aligning one circular hole 3a with the corresponding protruding portion 4a while positioning the hat-shaped cross-section part 1 with respect to the sheet-shaped member 2, the positions of the other circular hole 3b and the other protruding portion 4b become off from each other, as shown in FIGS. 10B and 10C. That is, it is no longer possible to ensure the accuracy of the relative positions of the circular holes 3a and 3b and the protruding portions 4a and 4b. 